Absorbent fibrous sheets and method of making same



Patented Nov. 1, 1949 ABSORBENT FIBROUS SHEETS AND METHOD OF MAKING SAME Raymond B. Seymour and George M. Schroder, Chattanooga, Tenn., assignors to Henry B. Frede and Company, Chattanooga, Team, a corporation of Tennessee No Drawing. Application June 14, 1946, Serial No. 676,861

8 Claims.

This invention relates to a sheet, made of unwoven fibrous material, which is suitable for use as toweling, surgical dressings, a diaper base and the like. More particularly, the invention pertains to a binding coating for such a sheet to hold the fibers against displacement and thereby form a strong fabric.

The invention concerns both the process of producing the coated sheet of loose fibrous mate rial, and the resulting article of manufacture.

It has been recognized, heretofore, that loose fibrous material in sheet form might be used for absorbent material such as towels and surgical dressings, if a binding material were applied to its surface. However, the past efforts to obtain a satisfactory product have not been entirely satisfactory either because the liquid absorbability of the sheeting has been seriously impaired, or because the binding material does not adequately tic together the fibers.

In those instances in the prior art in which a substantially continuous coating has been applied to the fibrous sheet for the purpose of retaining the surface fibers in position, the coating material has been of such a nature that it has resisted passage of moisture through it to the inner fibers of the sheet. Despite this drawback, the coating material has been applied as a continuous layer to secure the additional strengthening effect resulting from the web of coating material interconnecting the entire lengths of the portions of the fibers at the surface. No coating material has, however, been utilized which would satisfactorily absorb and transmit through it, the moisture with which it comes in contact.

To overcome the disadvantages arising from a continuous surface coating upon the fibrous sheet, it has heretofore been proposed that the binding material be restricted to localized portions only at the sheet surface. For example the binding material has been so applied that it becomes confined to the intersections of the fibers, the intervening portions of the fibers being free of binding material. In this instance, a binding material having a high strength and no capacity to absorb or transmit moisture may be used, but the resulting product has not been entirely satisfactory because it has lacked the desired strength. The fibrous material will readily absorb moisture because of the open or foraminous nature of the surface but due to the unconnected state of the major portion of the surface fibers they give a loose feel to the product and result in a weak structure.

The present invention overcomes the above and other disadvantages of the prior art. In accordance with the invention a substantially continuous surfacing layer of binding material is applied to a sheet of fibrous material and the resulting high strength of this construction is thereby obtained. According to an important feature of this invention, this surfacing material is made of a sodium salt of a carboxy alkyl derivative of cellulose, as it has been discovered that this compound if applied and treated in a certain way, will readily absorb and transmit through it, moisture applied to its exposed surface. The resulting product has a big str'engthcomparable to the strength of a woven abi ic, despite its formation of randoni disposed fibers. This high strength of the product is retained even after it becomes wet.

The fibrous sheeting employed to carry out the invention is preferably that obtained by picking apart woven, knitted or felted materials and garnetting these materials or virgin cotton or other cellulosic fibrous materials. In this process, an especially designed machine of known type, picks apart a woven, knitted or felted fabric and the picked material or virgin cotton or other fibrous material is formed into batting or felt of substantially uniform thickness in an especially designed machine termed a garnet. This fibrous sheet is economically produced when it is made from waste or rejected cellulosic or wool cloth. The cellulosic fibers may be either natural or synthetic.

The resulting sheet of fibrous material has the advantage over felt or batting produced by a carding process because its fibers are distributed in all directions in a random fashion. The uncoated fibrous sheet consequently has substan tially no tensile strength in any direction, but what strength it does possess is nearly uniform in all directions due to the irregular disposition of the fibers. This would not be true of a carded fabric as there the fibers are all lined up in the same direction.

The binding material of the invention is applied to the surface of this sheet of fibrous material. Although the sheet of irregularly arranged fibers is weak, it has sufilcient strength to be handled during application of this fiber binding material.

The coating material is applied as a dilute aqueous solution of a sodium salt of carboxy methyl cellulose and this may,'for example be a sodium salt of an ether formed by the reaction of alkali cellulose and monochloro acetic acid in such manner as to obtain a'product having from 0.2 to 1.0 glycolate groups per anhydro carboxy methyl cellulose for application to the fibrous sheet, is a 1% aqueous solution. Ex-

cellent results are however obtained with an aqueous solution of from 0.5 to 2.0%. This aqueous solution may be applied to the fibrous sheet in any appropriate manner which will form a substantially continuous layer, and one suitable way is by bringing the fibrous sheet into contact with a rotating roller upon which the solution is continuously sprayed. A film of the solution is thereby formed upon the roller and this film is transferred to the fibrous sheet as the sheet continuously comes into contact with the rotating roller.

1 After a film of the aqueous solution of the cellulose derivative is applied to the fibrous sheet, heat is applied to remove the water of solution. This heat is preferably applied by advancing the coated sheet to a rotating roller maintained at a temperature of from 300 to 450 F. This heated roller also serves to drive the coating material into the surface of the fibrous sheet.

It is important to heat the coating film to a temperature of from 300 to 450 F. to obtain the full benefits of the invention. By applying this moderately high heat the cellulose derivative becomes quite water insoluble but does not lose.

its capacity to absorb moisture. It is not deflnitely known why this heat changes the water soluble compound to an essentially water insoluble compound but one explanation is that the carboxyl group on the carboxy methyl cellulose reacts with a free hydroxyl group in an adjacent carboxy methyl cellulose molecule to form a compound having an apparent high molecular weight. This result is notobtained if heat of only 250 F. is applied. It is preferable that the cellulose derivative be applied in such quantity that it will be present in the range of from 0.25 to 0.4 pound per thousand square feet. This film thickness may be obtained byproperly relating the speed of travel of the fibrous sheet with respect to the quantity of coating material being delivered by the spray. If the fibrous sheet is to be used for toweling or like purpose, the binding coating should be applied to both sides of the material. Both sides of the product will then be water absorbent. However, if only one side of the fibrous sheet is to be water absorbent. as in the case of a diaper, the cellulosic derivative may be applied only to that side- A water proofing coating may be applied to' the other side if a diaper or like article is to be produced.

ing material, nearly all of the surface fiber portions are interconnected both at their points of intersection and along their intervening sections and this accounts for the resulting high strength. Also, the binding material penetrates somewhat into the sheet and binds together the fibers below the surface. I

The product has a soft feel and is pliable in the hands. It is non-toxic, and because of its smooth surface texture it may be brought into contact with the most sensitive tissues. It maintains, a high strength'after becoming wet and has a useful strength even in hot water.

The following tests illustrate some of the properties-of the material. A piece of felt 1" in cross section was placed between clamps and weights were added and the length of time for break was determined, the distance between the clamps being, 2". The untreated felt broke immediately when a 20 gram weight was added. The treated product was not broken in 10 seconds after the addition of a 500 gram weight.

- The sample was immersed in water and the test As a result of the application of the surface A disposed of after use and thus eliminate laundering expense. The water absorbability of the fibers is not impaired as the water rapidly penetrates through the coating. Due to the formation of asubstantially continuous film of the bindwas repeated. Under these conditions the sample did not break in 10 seconds after the addition of the 500 gram weight. The tests were repeated using strips cut at right angles to the previously described test pieces. and under these conditions similar results were obtained.

A piece of bonded cotton felt, measuring 3" x 4" and weighing 1 gram, was immersed in water for 10 seconds, placed on blotting paper for 5 seconds and reweighed. The total weight after this procedure was 11 grams, indicating that the material had absorbed 10 times its own weight of water. This test was repeated using a piece of absorbent woven cloth weighing 1 gram and the woven material gained 4 grams in weight due to the absorption of water.

The invention may be specifically illustrated by the following examples:

Example 1.-Waste cotton cloth is reduced to fiber form by the picking action of a garnetting machine, and the sheet obtained from this process is subjected to a spray on both sides with a 2% aqueous solution of carboxy methyl cellulose and subjected to a drying action of heated rolls at a temperature of 400 to 420 F. The treated product is then cut to size for disposable cloth napkins.

Example 2.Waste wool is used instead of the cotton cloth.

Example 3.Waste. viscose rayon is used in place of cotton cloth.

Example 4.-Waste viscose rayon cloth and waste cotton cloth are garnetted simultaneously on different machines, and the products are conveyed to a common apron so that the garnetted rayon and cotton are joined in sheet form, one surfacebeing extremely soft and water absorbent rayon and the other surface being cotton. This sheet is subjected to the same process as above.

Other suitable uses of the product of this invention, in addition to a towel and diaper, are for baby bibs, aprons, curtains, dress shields, table cloths, and clothing interliners.

What is claimed is:

1. A moisture absorbent article suitable for toweling, comprising a sheet of unwoven fibers having a random distribution and a coating consistlng entirely of a substantially continuous film of a sodium salt of a carboxy alkyl derivative of cellulose which is present as a dry, water-insoluble solid adhering to the fibers, said solid having .5 been made water-insoluble by subjecting it to a temperature of from 300 to 450 F.

2. A moisture absorbent article suitable for toweling, comprising a sheet of unwoven fibers having a random distribution and a coating consisting entirely of a substantially continuous film of a sodium salt of a carboxy alkyl derivative of cellulose which is present in the range of from 0.25 to 0.40 pound per thousand square feet adhering to the fibers as a dry, water-insoluble solid, said solid having been made water-insoluble by subjecting it to a temperature of from 300' to 450 F. e

3. A moisture absorbent article suitable for toweling, comprising a sheet of unwoven fibers having a random distribution and a substantially continuous coating consisting entirely of sodium carboxy methyl cellulose which is present as a dry, water-insoluble solid adhering to the fibers, said solid having been made water-insoluble by subjecting it to a temperature of from 300 to 450 F.

4. A moisture absorbent article suitable for toweling, comprising a sheet of unwoven fibers having a random distribution and a substantially continuous coating consisting entirely of sodium carboxy methyl cellulose adhering to the fibers as a dry, water-insoluble solid, said solid having been made water-insoluble by subjecting it to a temperature of from 300 to 450 F., and said coating being present in the range of from 0.25 to 0.40 pound per thousand square feet.

5. The process of making a moisture absorbent article suitable for toweling which comprises applying to a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of a sodium salt of a carboxy alkyl derivative of cellulose, and applying heat within the range 300 to 450 F. to expel the water of solution and convert the cellulose derivative to an essentially water insoluble product.

6. The process of making a moisture absorbent article suitablefor toweling which comprises applying to a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of a sodium salt of a carboxy alkyl derivative of cellulose, and applying heat within the range of 300 to 450 F. to expel the water of solution and convert the cellulose derivative to an essentially water insoluble product, said solution being applied in the quantity to yield a film of the cellulose derivative in the range of from 0.25 to 0.40 pound per thousand square feet.

7. The process of making a moisture absorbent article suitable for toweling which comprises applying to a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of sodium carboxy methyl cellulose, and heating to a temperature of from 300 to 450 F. to produce an essentially water insoluble film.

8. The process of making a moisture absonbent article suitable for toweling which comprises applying to a sheet of unwoven fibers having a random distribution, a substantially continuous coating of a 0.5 to 2.0% aqueous solution of sodium carboxy methyl cellulose, and heating to a temperature of from 300 to 450 F. to produce an essentially water insoluble film having a thickness in the range of from 0.25 to 0.40 pound per thousand square feet.

RAYMOND B. SEYMOUR.

GEORGE M. SCHRODER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,087,237 Bolton July 20, 1937 2,235,798 Collings et al Mar. 18, 1941 2,297,698 Freeman Oct. 6, 1942 2,370,517 Bass Feb. 27, 1945 

